arecord, convert: edit pages

pages/common/convert.md

@@ -16,9 +16,9 @@
 
 `convert {{path/to/input_image.png}} -resize 640x480 {{path/to/output_image.png}}`
 
-- Horizontally append images:
+- Scalte an image to have a certain filesize:
 
-`convert {{path/to/image1.png path/to/image2.png ...}} +append {{path/to/output_image.png}}`
+`convert {{path/to/input_image.png}} -define jpeg:extent=512kb {{path/to/output_image.jpg}}`
 
 - Vertically append images:
 

pages/linux/arecord.md

@@ -22,3 +22,7 @@
 - Allow interactive interface (e.g. use space-bar or enter to play or pause):
 
 `arecord --interactive`
+
+- Test your microphone:
+
+`arecord -d 5 test-mic.wav && aplay test-mic.wav && rm test-mic.wav`